Sound recording



G. L. DIMMlcK souNn nEconnnxe Filed Fb. 2e. 195e May 7, 1940.

2 sheets-sheet 1 May 7 1940- s. L. DIMMlcK 2.199.621

SOUND RECORDING Filed Feb. 28. 193e' 2 sheets-sheet 2 Patented May 7, 1940 SOUND RECORDING Glenn L. Dmmick, Haddonield, N. J., assigner to Radio Corporation Iof America, a corporation of Delaware Application February 28, 1938, Serial No. 193,130

7 Claims'.

This invention relatesto an improved sound record and method of and apparatus for making the same, and is an improvement on the method and apparatus shown and described in my application Serial No. 125,544, led February 13,

The sound record in accordance with my invention has, in the positive, extremely dark areas symmetrically arranged in relation to the axis of the sound track and corresponding to the Aenvelope of the sound waves being recorded. Between the dark areas lie the sound records, each of which, in turn, is symmetrical about its own axis or represents a symmetrical modulation are indicated by a portion having an optimum density for proper resolution against a clear background, thereby producing a sound record which will give the most satisfactory reproduction of the sound waves at all amplitude levels and due to the eXtreme density of the background with a minimum of ground noise. The negative sound records are, of course, the converse of the positive sound record. The sound records which may be produced in accordance with my invention may be of either of the types known commercially as Doubly modulated Class A pushpull or Class B push-pull.

In the recording apparatus I use a modication having a ground noise reduction shutter and with the parts so modified and rearranged that the about that axis and in which the sound WavesI of a commercial type of variable area recorder ground noise reduction shutter defines the clear 4portions of the negative defining the black portions of the print. The galvanometer' mirror moves the main recording beam producing the black portions of the negative and the clear portions of the print in the usual manner and on this latter exposure, but masked by the shutter, is superposed a light of uniform intensity reflected by the cover glass of the galvanometer.

One object of my present invention is to provide an improved sound recording apparatus.

Another object of my present invention is to provide an improved type of ground noise reduction shutter.

Another object of my present invention is to provide a sound recording optical system in which the light reflected from the cover glass of the galvanometer is used and not wasted. Another object of my present invention is to provide an improved optical system wherein the light reflected by the cover glass of the galvanometer is usefully superposed upon the light reflected from the galvanometer mirror.

Another object of my presentinvention is to provide an improved type of sound record.

Another object of my present invention is to provide an improved type of Class A push-pull ,Y

sound record.

Another object of my present invention is to provide an improved type of Class B push-pull y sound record.

Other and incidental objects of my invention will be apparent tovthose skilled in the art from lo a reading of the following specification and an inspection Aof the accompanying drawings in which Figure 1 is a perspective schematic view of my improved optical system, 15'

Figure 2.y shows the position of the shutter vane in relation to the slit,

Figure 3 shows the position of the fogging beam alni the recording light beam in relation to the s 1 Figure 4 shows the type of negative sound record produced by the apparatus as shown in Figs. 1, 2 and 3,

"Figure 5 shows a positive sound record as printed from the negative sound record of Fig. 4, 25

Figure 6 shows the relation of the fogging beam and modulation beam to the slit for Class A push-pull recording,

Figure 7 shows a negative sound record as produced by the arrangement shown in Fig. 6, 30

Figure 8 shows a positive sound record as printed from the negative sound record of Fig. 7,

Figure 9 shows the arrangement of the fogging beam and modulation recording beam for making a Class B push-pull sound record, Y 35 Figure 10 shows a negative Class B push-pull sound record as made with the arrangement shown in Fig. 9, and

Figure 11 shows a positive Class B push-pull record. as printed from the negative of Fig. 10.

Referring iirst to Fig. l, light from the source I0 passes through the condenser lens II, and the aperture I2 and the mask I3 to the lens I4, Whichwith the lens Il forms an image of the 45 filament oi the lamp I0 upon the galvanometer mirror I5. The light reflected by the mirror I5 passes through the lens I6 to the slit plate I8. upon which an image of the aperture I2 is formed by the action of the lens I land I6. Light passing 50 through the slit I 1 in the slit plate I8 is then focussed upon the film 20 by the lens I9. The image produced upon the slit plate IB by the aforesaid apparatus has the form shown at IZA in Fig. 3 and the operation of the apparatusuthus 5,6

far is substantially identical with that shown in my Patent No. 1,199,721.

'Ihe galvanometer having the mirror I5 is provided with a cover plat-e 24, as is customary. However, the cover plate on the usual galvanometer is inclined at such an angle as to divert any rays reflected by it from the optical axes and thereby prevent any of this light from reaching either the slit Ii or the lm 23. In the present apparatus, the cover plate 2s is located substantially perpendicular to the bisector of the angle between the two optical axes, and a secondary image of the aperture 12 is, therefore, reected upon the slit plate i8, as indicated at I2B. `Since the light reflected from the front and back surfaces of the cover plate 3d is of the order of 8% or 10% of the incident light, the image I 2B will be of correspondingly less intensity than the image at I2A, and this image IZB will remain stationary in relation to the slit, while the image IZA will vibrate in accordance with the sound waves being recorded. Although the light normally reected from the cover plate is, as stated above, from 8% to 10% of the incident light, this refiected light may be increased as desired by thinly aluminizing or otherwise providing a partly-reflecting coating on one or both of the surfaces of the cover plate 2d, taking into due account, of course, the fact that increase of reection from the cover plate correspondingly decreases the light transmitted to the galvanometer mirror itself. The arrangement thus far described would produce a sound record having a minimum density determined by the brightness of the image I 2B and having a maximum density determined by the sum of the brightness of the image IZA and the image I2B.

Both the images IZA and I 2B are, of course, intercepted by the shutter 2i producing corresponding clear portions in the negative record. As shown in Fig. 2, when there is no current passed through the shutter motor 23, i. e., when the shutter is unbiased, it is in the position ZI with the tips of the triangular portions of the shutter just covering the slit I'! and producing the narrow clear portions shown at 33 and 3l in Fig. 4 on the negative. When biasing current is applied to the shutter motor 23, if there is no modulation, the shutter moves downward to the position ZIA` when only a narrow portion of the slit I'l is not obscured by the shutter and narrow exposed areas as indicated at 32 and 33 in Fig. 4 are produced. In the normal operation of the ground noise reduction amplifier, the bias current is decreased, as the signal strength is increased, and therefore on a loud signal the shutter moves back to the position indicated at 2 I, Fig. 2, thereby producing the wide exposed portions between the narrower portions 33 and 3l. In this case, however, the amplitude of movement of the light beam IZA has increased, at the same time producing a dark negative sound record as indicated at 34 and 35 in Fig. 4 against the gray background, as indicated at 33 and 37, which is produced by the auxiliary light beam I2B.

When the negative of Fig. clis printed in the customary printer having an exposure aperture of definite width, the exposure aperture defines the edges 40 and 4I of the sound track area and the marginal portion within these edges is eX- posed to a very high density of approximately 2.0

no audible effect on the reproduction of sound from the print. The middle portion 44 of the sound record corresponding to the middle clear portion of the negative is, of course, printed in to the same high density as the marginal portions. The sound record portions corresponding to the darker portions 34 and 35 of the negative are left perfectly clear, as indicated at 4S and 41, while the gray portions 3@ and 3'! of the negative print gray of a density of about 1.3 in the portion indicated at 48 and 49. 'Ihis density of 1.3 against a clear background is the most desirable for high frequency resolution, to prevent Zero shift and for the other photographic reasons incidental to the reproduction of sound records, but, on the contrary, this density is not most conducive to fogging in of dust spots and the like. The high density of 2.0 which satisfactorily fogs in the dust spots would, on the other hand, fog in high frequency records just as effectively as it would dust spots, and this portion having a density of 1.3 is, accordingly, restricted to a minimum by the envelope exposure having a density of 2.0 indicated at 42, 43 and 44.

A modification of the apparatus for application to Class A push-pull recording is illustrated in Fig. 6. In this case, the aperture I2 in the mask I3 is so shaped as to produce two complementary light beam portions I) and 5I, as described and claimed in my application Serial No. 137,905, led April 20, 1937. The light spot however, differs from that in the aforesaid application in that it is provided with a rectangular extension 52. These light beams 53 and 5I extend over the recording slit Il' in the relation indicated in Fig. 6 and are simultaneously and similarly moved in the same direction to produce the Class A push-pull sound record described in said application, but the images 53A and SIA produced by reflection from the galvanometer cover glass are so displaced that the portion 52A together with the base of the portion 5IA cover the slot I'I uniformly. This arrangement is used in the apparatus shown in Fig. 1, including the shutter, and the negative record shown in Fig. l is thereby produced having the gray portions 30 and 3I produced by the shutter, the heavily exposed portions 34 and 35 produced by the recording beams 50 and 5I plus the auxiliary exposure at 52A and the sound wave exposure 36 and 31 having the density of approximately 1.3, as described above. It will be apparent that this negative sound track differs .from that shown in Fig. 4 in that the opposite halves of the sound wave are 180 degrees out of phase and when printed upon a positive, as shown in Fig. 8, the parts of which correspond with the parts indicated by corresponding reference numerals in Fig. 5, a record is produced which can be reproduced only in a push-pull reproducer, but which has the advantages inherent in a push-pull record and, in addition, has the advantages pointed out above for the record of Fig. 5.

In order to produce. what is known as a Class B push-pull sound record in which neither half of the sound track includes a complete wave record, but the two halves contain complementary records as described and claimed in my Patent No. 2,093,423, I employ the aperture arrangement shown in Fig. 9 where the mask I3 is provided with exposed triangular apertures so shaped that the beam incident on the slit Il will include opposed triangular portions 60 and 6I having their apices in the unmodulated portion coincident with the slit. The beam also includes extensions 62 and 53 from these apices producing a narrow black line on the negative and a corresponding narrow transparent line on the print to prevent wave shape distortion as described and claimed in my U. S. Patent No. 2,097,657, issued November 2, 1937. In order to produce the auxiliary exposure in this form of the invention, I provide a rectangular extension 64 on the portion of the beam indicated at B similar to the extension 52 in Fig. 6 and the galvanometer cover is so tilted that this portion of the light beam is reflected on the slit l1, as indicated at 64A. In this instance, the extension 62 and 63 of the light beams produce the complementary half wave exposures of high density 36 and 31, Fig. l0, and the portion of the beam of lower intensity 64 produces the surrounding gray envelope 34 and 35. A print of this negatve of Fig. 10 is shown in Fig. 11, Where it will be seen that the narrow axial exposures 62A and 63A produce narrow clear lines in the print, as indicated at 62A and 63B, while the several portions 42 to 49 bear the same relation to the corresponding portions of theA negative of Fig. 10 that these portions in the print of Fig. bear to the negative of Fig. 4.

In the negative record produced as above described, I prefer to so adjust the exposure light and the reflecting power of the galvanometer cover glass that the high density portions of the v negative have a density of approximately 2.4,

while the gray portions have a .density of approximately .4, which relation of densities serves to produce satisfactory prints of thedensities referred to above.

My invention, of course. is not limited to the use of the specific densities referred to in either positive or negative film.

It will be apparent to those skilled in the art that my invention is not limited to the specific apparatus and purposes shown, but that the shape of both the beam-defining vaperture and the ground noise reduction shutter may be varied at will so long as their relative functions remain as hereinbefore described. It will be also apparent that I may use a shutter of the type referred to in conjunction with the aperture without using the reflected beam from the galvanometer cover, as described, and it will be apparent that the relative shapes of the shutter edge and of the aperture may be varied as desired so as to properly correlate the several functions. For example, the aperture l2 may be corrected in shape to compensate for characteristics of the recording amplifier and the lcontour of the effective edge of the shutter 2l may be calculated to compensate both for the shape of the aperture l2 and for the characteristics of the ground noise reduction amplifier. Similarly, either or both of these elements may be varied in contour to correct for the lack of uniformity of illumination in the optical system so asv to produce a uniformity in the sound record produced irrespective of the deficiencies of the sound recording.v

electrical or optical systems or of the ground noise reduction electrical system.

Having now described my invention, I claim: 1. Sound recording apparatus including illumiv nating means, means for directing light from said illuminating means through an aperture defining the shape of the recording beam, means for directing said beam to a slit, means for vibrating a portion of said beam at vsaid slit, meansffor directing another portion of said beam to said slit independently of said vibrating meansjmeans for obsouring predetermined areas of both said portions of said beam at said slit, and means for imaging the light passing through said slit upon av recording medium. f

2. Sound recording apparatus including illuminating means, means for directing light from said illuminating means through an aperture defining the shape Aof the recording beam, means for directing said beam to a slit, vmeans for vibrating a portion of said beam at said slit, partially reecting means for directing another portion of said beam to said slit independently of said vibrating means, means for obscuring pre,-` determined areasl of both said portions of said beam at said slit, and means for imaging the light passing through said slit upon a recording medium.

3. The method of sound recording comprising directing a beam of light toward a film, directing a second beam of light of predetermined contour toward the lm, vibrating said second beam in accordance with sound to be recorded, and intercepting portions of both of said beams in accordance with the envelope of the sound to be recorded.

4. The method of sound recording comprising directing a beam of light toward a film, directing a second coincident beam of light of predetermined contour toward the film, vibrating said 'second beam in accordance with sound to be recorded, and intercepting portions of both of said beams in accordance with the envelope of the sound to be recorded.

5. 'I'he method of sound recording comprising directing a beam of light toward a film, directing a second beam of light of predetermined contour toward the nlm, vibrating said second beam in accordance with sound to be recorded, and intercepting portions of both of said beams in accordance with the envelope of the sound to be recorded, the first of said beams before interception being of such size as to expose the entire width of the record area.

6. The method of sound recording comprising directing a beam of light toward a lm, directing a second beam of light of predetermined contour and greater intensity toward the film, vibrating said second beam in accordance with sound to be recorded, and intercepting portions of both of said beams in accordance with the envelope of the sound to be recorded.

'7. The method of sound recording comprising directing a beam of light toward a lm, directing a second beam of light of predetermined contour and greater intensity toward the 1m,'vibrating said second beam in accordance with sound'to be recorded, and intercepting coincident portions of both of said beams in accordance with the envelope of the sound to be recorded.

GLENN L. DIMIIVIICK. 

